Wireless Communication Terminal and Control Method Threrof

ABSTRACT

In a PC card communication terminal that operates supplied with power from a host device, problems such as malfunctions due to a supply voltage drop at the time of high transmission output are prevented from occurring. A baseband processor ( 1106 ) selects a transmission-power upper-limit measurement mode when a PC card terminal ( 1103 ) is to be controlled for the first time. A supply voltage drop is measured by a voltage measurement circuit ( 1114 ) while a load value of a load circuit ( 1112 ) is being changed. The load value of the load circuit ( 1112 ) when the supply voltage decreases to a permissible lowest supply voltage is obtained. Using a conversion table stored in a memory ( 1107 ), the load value is converted into a transmission output and is set as a transmission-output upper limit. In a normal communication mode, a maximum transmission output is restricted based on this transmission-output upper limit.

TECHNICAL FIELD

The present invention relates to a technique for controlling wirelesscommunication terminals that are mounted in host devices and suppliedwith power from the host devices for operation. In particular, thepresent invention relates to a technique for increasing the operatingreliability of a wireless communication terminal by preventing thewireless communication terminal from, for example, malfunctioning due toa drop in supply voltage at the time of high transmission output.

The present application claims the benefit of priority from JapanesePatent Application Nos. 2004-223836, 2004-223837, and 2004-223838 filedJul. 30, 2004, the contents of which are incorporated herein byreference.

BACKGROUND ART

In response to recent increasing demands for the capability of datacommunication in mobile phone systems, a growing number of card datacommunication terminals are being used.

While known mobile phone terminals are supplied with power from built-inbatteries for operation, PC card (PCMCIA card) terminals are typicallysupplied with power by host devices, such as personal computers, becausethese PC card terminals do not have batteries therein due to, forexample, a size restriction.

Card slots for PC cards are typically provided in portable terminalssuch as so-called notebook PCs and PDAs (personal informationassistants). Electrical characteristics such as signals and power supplyand mechanical characteristics such as size in these card slots arespecified as standards (as in the PC Card Standard by the standardsorganizations PCMCIA in the USA and JEITA). PC card terminals alsocomply with these standards. The standard for power supply specifies 3.3V±0.3 V and a maximum of 1 A for 32-bit cards (Card Bus), for example.

In wireless communication techniques supporting recent high datacommunication speeds and cellular systems, unlike wireless LANs, assumedto be used in wide areas (e.g., CDMA2000 and W-CDMA), basebandprocessors such as high-speed CPUs and maximum transmission powers of 20dBm (100 mW) or more are required, which leads to more powerconsumption. For example, in device types that employ the CDMA2000 1×technique and are rated a maximum transmission power of 23 dBm, even PCcard terminals that do not have, for example, LCDs (liquid crystaldisplays) or backlight may exhibit a consumption current of about 1 A atthe time of maximum output transmission.

For communication techniques in which terminal transmission power iscontrolled by a base station, such as the CDMA2000 1× technique,terminals perform transmission with the minimum required transmissionpower. More specifically, radio waves from a terminal located near abase station easily reach the base station, and therefore, such aterminal performs transmission (communication) with a low output. On theother hand, a terminal located distant from a base station performstransmission (communication) with a high output, which causes thecurrent consumption to increase.

In view of these circumstances, a communication technique for reducingpower consumption of mobile communication terminals is proposed, asdescribed in, for example, Patent Document 1. In this technique, when amobile communication terminal detects a drop in supply voltage, thenetwork is informed of the fact, and a value smaller than normal isdetermined anew as the maximum transmission power required to continuecommunication.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2003-309516

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In some commercially available portable terminals having card slots, thevoltage of the card slots is lower than the standard value becausepriority is given to the operation time of the battery, or the voltagefalls below the standard value at the time of high electric current(about 1 A) due to the capability of supplying electric current.

For this reason, depending on the device type of portable terminals,when a PC card terminal performs transmission (communication) with themaximum output, high electric current flows and the voltage at the PCcard slot falls below the operating voltage range (normally incompliance with the standard) of the PC card terminal. This disablescommunication from continuing because the PC card terminal operatesunstably or is reset due to the voltage drop, even though the PC cardterminal itself meets the specifications of the standards.

This problem is addressed by the PC-card-terminal manufacturers thatconduct compatibility (affinity) tests between the PC card terminal and,for example, commercially available portable terminals to disclose alist of, for example, operation-confirmed device types. However,non-listed portable terminals need to be tested by users themselves tosee if compatibility is achieved by performing, for example, anoperational check. If the operation is problematic as a result of suchan operational check, it is difficult to use the PC card terminal. Morespecifically, a burdensome measure such as connecting a power cable tobe connected to another power supply port (e.g., USB or PS/2 port) ofthe portable terminal and connecting an AC adaptor is required. What isworse, it is not possible to operate the PC terminal card if such ameasure is not available.

The technique described in Patent Document 1 is mainly intended toaddress the problem of a time-lapse voltage drop due to batteryconsumption during communication, rather than the above-describedproblems. Furthermore, the same technique is not satisfactory as acountermeasure against an abrupt voltage drop produced when hightransmission power occurs suddenly (e.g., when communication starts orhigh transmission power is required because of an object interferingwith the base station during mobile communication).

The present invention has been conceived in light of these circumstancesand is related to a wireless communication terminal which is mounted ina host device, such as a portable terminal, and supplied with power fromthe host device for operation. An object of the present invention is toincrease the operating reliability of such a wireless communicationterminal by eliminating the risk of the wireless communication terminalmalfunctioning at the time of high transmission power due to a drop involtage.

Means for Solving the Problems

In order to solve the above-described problem, a method of controlling awireless communication terminal according to a first aspect of thepresent invention is a method of controlling a wireless communicationterminal that is supplied with power supply from a host device foroperation, in which the wireless communication terminal is mounted inthe host device. This method includes the steps of measuring a voltageof the power supply; setting a transmission-output upper limit based onthe voltage; and restricting a maximum transmission output based on thetransmission-output upper limit.

In a second aspect of the present invention, the method of controlling awireless communication terminal according to the first aspect of thepresent invention includes the step of measuring a drop in the voltagecorresponding to current consumption while transmission is not beingperformed. In the step of setting the transmission-output upper limit, atransmission output that occurs when the voltage decreases to a presetpermissible lowest voltage is obtained to set the transmission output asthe transmission-output upper limit.

In a third aspect of the present invention, the method of controlling awireless communication terminal according to the second aspect of thepresent invention is characterized in that in the step of measuring thedrop in the voltage, the drop in the voltage is measured via a loadvalue of a load circuit, the load value being variable, while thevoltage is applied to the load circuit, and in the step of setting thetransmission-output upper limit, the transmission-output upper limit isset by converting the load value into a transmission output.

In a fourth aspect of the present invention, the method of controlling awireless communication terminal according to the second aspect of thepresent invention is characterized in that in the step of measuring thedrop in the voltage, the drop in the voltage is set by measuring thedrop in the voltage with a terminating circuit for terminating atransmission output being connected to a transmission circuit.

In a fifth aspect of the present invention, the method of controlling awireless communication terminal according to the first aspect of thepresent invention is characterized in that the wireless communicationterminal includes a transmission-output upper-limit mode in which thetransmission-output upper limit is set and the set transmission-outputupper limit is transmitted to the host device and saved; and a normalcommunication mode in which the maximum transmission output isrestricted based on the transmission-output upper limit received fromthe host device. One of the transmission-output upper-limit mode and thenormal communication mode is selected.

In a sixth aspect of the present invention, the method of controlling awireless communication terminal according to the first aspect of thepresent invention is characterized in that in the step of measuring thevoltage, the voltage is measured during transmission operation toacquire voltage measurement values corresponding to differenttransmission output values. Furthermore, the method includes the stepsof converting the transmission output values into current consumptionvalues; and estimating a current consumption value corresponding to apreset permissible lowest voltage based on the voltage values and thecurrent consumption values. In addition, in the step of setting thetransmission-output upper limit, the estimated current consumption valueis converted back into a transmission output value to set thetransmission output value as the transmission-output upper limit.

In a seventh aspect of the present invention, the method of controllinga wireless communication terminal according to the first aspect of thepresent invention is characterized in that in the step of measuring thevoltage, transmission operation is performed with a transmission outputlower than a transmission output requested at the time of a firsttransmission operation, and subsequently, the voltage measurement valuesare acquired while the transmission output is increased in a stepwisemanner.

In an eighth aspect of the present invention, the method of controllinga wireless communication terminal according to the first aspect of thepresent invention is characterized in that in the step of measuring thevoltage, a voltage value of the power supply is measured duringtransmission operation, and in the step of setting thetransmission-output upper limit, a transmission output value duringtransmission operation exhibited when the measured voltage value fallsbelow a threshold value larger than a preset permissible lowest voltagevalue is set as the transmission-output upper limit.

In a ninth aspect of the present invention, the method of controlling awireless communication terminal according to the first aspect of thepresent invention is characterized in that a maximum transmission outputvalue with which transmission has been performed is stored as a maximumtransmission-output history value before the step of measuring a voltagevalue of the power supply; and if a transmission output with whichtransmission is to be performed exceeds the maximum transmission-outputhistory value, the transmission output is restricted to a value producedby adding a predetermined increment value to the maximumtransmission-output history value, and after the transmission, themaximum transmission-output history value is updated.

A tenth aspect of the present invention provides a program for awireless communication terminal to achieve the method of controlling awireless communication terminal according to the first aspect of thepresent invention.

An eleventh aspect of the present invention is a wireless communicationterminal mounted in a host device and supplied with power supply fromthe host device for operation. This wireless communication terminalincludes a supply-voltage measurement section for measuring a voltagevalue of the power supply; a transmission-output upper-limit settingsection for setting a transmission-output upper limit based on thevoltage value; and a transmission-output control section for restrictinga maximum transmission output based on the transmission-output upperlimit.

In a twelfth aspect of the present invention, the wireless communicationterminal according to the eleventh aspect of the present inventionincludes a load circuit having a variable load value; apower-supply-connection switching section for switching a connection ofthe power supply between a transmission circuit and the load circuit; aload-value setting section for determining a load value exhibited whenthe voltage measured by the supply-voltage measurement section while theload value of the load circuit is being changed decreases to a presetpermissible lowest voltage value; and a transmission-output upper-limitconversion section for converting the load value determined by the loadsetting section into the transmission-output upper limit based on aconversion table of a preset load value and the transmission-outputupper limit.

In a thirteenth aspect of the present invention, the wirelesscommunication terminal according to the eleventh aspect of the presentinvention includes a terminating circuit for terminating a transmissionoutput; and an output-stage switching section for switching a connectionof an output stage between an antenna and the terminating circuit. Inthis wireless communication terminal, the transmission-outputupper-limit setting section determines, as the transmission-output upperlimit, a transmission output value exhibited when the voltage measuredby the supply-voltage measurement section while the transmission outputis being changed decreases to a preset permissible lowest voltage value.

In a fourteenth aspect of the present invention, in the wirelesscommunication terminal according to the eleventh aspect of the presentinvention, the supply-voltage measurement section measures voltagevalues corresponding to different transmission output values duringtransmission operation. This wireless communication terminal includes atransmission-output/current relationship storage section storing acorrespondence between a transmission output and current consumption;and a current-consumption-value estimation section for estimating acurrent consumption value corresponding to a preset permissible lowestvoltage value based on the measured voltage values and currentconsumption values obtained by converting the transmission output valuesusing the correspondence in the transmission-output/current relationshipstorage section. Furthermore, in this wireless communication terminal,the transmission-output upper-limit setting section converts the currentconsumption value estimated by the current-consumption-value estimationsection back into a transmission output value to set the transmissionoutput value as the transmission-output upper limit.

In a fifteenth aspect of the present invention, in the wirelesscommunication terminal according to the eleventh aspect of the presentinvention, the supply-voltage measurement section measures voltagevalues corresponding to different transmission output values duringtransmission operation, and the transmission-output upper-limit settingsection sets, as the transmission-output upper limit, a transmissionoutput value during transmission operation exhibited when the measuredvoltage value falls below a threshold value larger than a presetpermissible lowest voltage value.

Advantageous Effects of the Invention

As described above, according to the present invention, atransmission-output upper limit up to which the wireless communicationterminal can operate normally is set assuming power supplied from thehost device, and the maximum transmission output of the wirelesscommunication terminal is restricted based on this transmission-outputupper limit. Therefore, even if the performance of power supplied fromthe host device is low, transmission operation can be performed withinan output range adjusted to the performance of the power supply. Thisprevents the wireless communication terminal from exhibiting an abnormaloperation or experiencing shutdown or communication breakdown, therebyenhancing the operating reliability. Therefore, irrespective of atransmission output increased by an abrupt change in communicationenvironments, the operating reliability is prevented from decreasing.

Furthermore, since the transmission-output upper limit is set inaccordance with the actual performance of the power supplied from thehost device to the wireless communication terminal, a problem withcompatibility in power supply performance between the host device andthe wireless communication terminal can be overcome, thereby eliminatingthe burden of conducting a compatibility test. Moreover, even in a casewhere the conventional wireless communication terminal could not be usedas-is due to insufficient power supply performance, the wirelesscommunication terminal can now be used without the burdensome work ofsecuring power for the wireless communication terminal by connecting toanother power supply port using, for example, a connection cable.

In addition, a transmission-output upper limit can be obtained withoutrequiring a high-output transmission operation by applying supplyvoltage to a load circuit with variable load values or measuring thedrop in supply voltage while a terminating circuit is connected to theoutput stage of the wireless communication terminal.

Furthermore, according to the structure where the above-described loadcircuit is employed, since it is not necessary to provide, for example,a switching element at the output stage of the wireless communicationcircuit, the present invention can be applied without causing loss atthe output stage.

In addition, according to the structure where the terminating circuit isconnected to the output stage of the wireless communication terminal, itis not necessary to prepare, for example, a load circuit separately fromthe wireless communication circuit. This affords an advantage in thatthe present invention can be applied on a small circuit scale.

Furthermore, the wireless communication terminal measures thetransmission-output upper limit upon receiving an instruction from thehost device, whereas the host device saves the transmission-output upperlimit acquired from the wireless communication terminal. In this manner,transmission-output upper limit measurement operation by the wirelesscommunication terminal can be minimized by supplying the savedtransmission-output upper limit to the wireless communication terminalfor communication processing during normal operation and, as required,by instructing the wireless communication terminal to measure atransmission-output upper limit. By doing so, a time loss accompanyingtransmission-output upper-limit measurement operation is suppressed,thereby affording an advantage in that if the host device is driven on abuilt-in battery, saving in the built-in battery is achieved.

In addition, according to the present invention, a transmission-outputupper limit up to which the wireless communication terminal can operatenormally is set assuming power supplied from the host device, and themaximum transmission output of the wireless communication terminal isrestricted based on this transmission-output upper limit. Therefore,even if the performance of power supplied from the host device is low,transmission operation can be performed within an output range adjustedto the performance of the power supply. This prevents the wirelesscommunication terminal from exhibiting an abnormal operation orexperiencing shutdown or communication breakdown, thereby enhancing theoperating reliability. Therefore, irrespective of a transmission outputincreased by an abrupt change in communication environments, theoperating reliability is prevented from decreasing.

Furthermore, since the transmission-output upper limit is set inaccordance with the actual performance of the power supplied from thehost device to the wireless communication terminal, a problem withcompatibility in power supply performance between the host device andthe wireless communication terminal can be overcome, thereby eliminatingthe burden of conducting a compatibility test. Moreover, even in a casewhere the conventional wireless communication terminal could not be usedas-is due to insufficient power supply performance, the wirelesscommunication terminal can now be used without the burdensome work ofsecuring power for the wireless communication terminal by connecting toanother power supply port using, for example, a connection cable.

Furthermore, supply voltage is measured during transmission operation toacquire supply voltage measurement values at different transmissionoutputs, and from these supply voltage measurement values a currentconsumption value corresponding to the permissible lowest supply voltagevalue is estimated to set a transmission-output upper limit. Therefore,a transmission-output upper limit can be obtained without high-outputtransmission operation.

In addition, if transmission operation is carried out with a lowtransmission output regardless of the transmission output requested atthe time of the first transmission operation, the subsequenttransmission operation is carried out while the transmission output isbeing increased in a stepwise manner, and supply voltage measurementvalues are acquired during these transmission operations, then atransmission-output upper limit can be set based on information acquiredduring actual transmission operation. This eliminates the need foradding, for example, transmission operation for the purpose of acquiringa transmission-output upper limit. Moreover, it is possible to prevent,for example, the wireless communication terminal from being reset as aresult of a high transmission output being requested before atransmission-output upper limit is determined.

In addition, since even a host device with low power supply performancecan assure the wireless communication terminal of operating reliability,and furthermore, only a small amount of electrical power is sufficientto acquire a transmission-output upper limit, PC-card built-in wirelesscommunication terminals that can be mounted in PC card slots providedmainly in portable information terminals are preferably applicable.

In addition, according to the present invention, a transmission powerupper limit up to which the wireless communication terminal can operatenormally is set assuming power supplied from the host device, and themaximum transmission power of the wireless communication terminal isrestricted based on this transmission power upper limit. Therefore, evenif the performance of power supplied from the host device is low,transmission operation can be performed within all output range adjustedto the performance of the power supply. This prevents the wirelesscommunication terminal from exhibiting an abnormal operation orexperiencing shutdown or communication breakdown, thereby enhancing theoperating reliability. Therefore, irrespective of transmission powerincreased by an abrupt change in communication environments, theoperating reliability is prevented from decreasing.

Furthermore, since the transmission power upper limit is set inaccordance with the actual performance of the power supplied from thehost device to the wireless communication terminal, a problem withcompatibility in power supply performance between the host device andthe wireless communication terminal can be overcome, thereby eliminatingthe burden of conducting a compatibility test. Moreover, even in a casewhere the conventional wireless communication terminal could not be usedas-is due to insufficient power supply performance, the wirelesscommunication terminal can now be used without the burdensome work ofsecuring power for the wireless communication terminal by connecting toanother power supply port using, for example, a connection cable.

In addition, a threshold with a margin for the permissible lowest supplyvoltage value is preset and supply voltage is measured duringtransmission so that when the supply voltage measurement value fallsbelow the threshold, the transmission power during the transmission isset to the transmission power upper limit. For this reason, atransmission power upper limit can be obtained without high-outputtransmission operation.

Furthermore, if transmission is carried out with low transmission powerregardless of the transmission power requested during transmission andthe subsequent transmission operation is carried out while thetransmission power is being increased in a stepwise manner to update themaximum transmission power history value, then it is possible toprevent, for example, the wireless communication terminal from beingreset as a result of high transmission power being requested before atransmission power upper limit is determined.

In addition, since even a host device with low power supply performancecan assure the wireless communication terminal of operating reliability,and furthermore, only a small amount of electrical power is sufficientto acquire a transmission power upper limit, PC-card built-in wirelesscommunication terminals that can be mounted in PC card slots providedmainly in portable information terminals are preferably applicable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram depicting the structure of a PC cardcommunication terminal according to a first embodiment of the presentinvention.

FIG. 2 is a circuit diagram depicting one specific example of a loadcircuit according to the present invention.

FIG. 3 is a flowchart illustrating the main part for communicationcontrol according to the first embodiment of the present invention.

FIG. 4 is a block diagram of a PC card communication terminal accordingto a second embodiment of the present invention.

FIG. 5 is a circuit diagram depicting one specific example of aterminating circuit according to the present invention.

FIG. 6 is a flowchart illustrating the main part for communicationcontrol according to the second embodiment of the present invention.

FIG. 7 is a schematic block diagram depicting the structure of a PC cardcommunication terminal according to a fourth embodiment of the presentinvention.

FIG. 8 is a flowchart illustrating the main part for communicationcontrol according to the fourth embodiment of the present invention.

FIG. 9 is a diagram depicting a table indicating the correspondencebetween transmission power and current consumption.

FIG. 10 is a graph showing the relationship between supply voltage andcurrent consumption.

FIG. 11 is a flowchart illustrating the main part for communicationcontrol according to a fifth embodiment of the present invention.

FIG. 12 is a flowchart illustrating the main part for communicationcontrol according to a sixth embodiment of the present invention.

FIG. 13 is a graph depicting one example of communication processingaccording to the sixth embodiment of the present invention.

FIG. 14 is a schematic block diagram depicting the structure of a PCcard communication terminal according to a seventh embodiment of thepresent invention.

FIG. 15 is a flowchart illustrating the main part for communicationcontrol according to the seventh embodiment of the present invention.

FIG. 16 is a flowchart illustrating the main part for communicationcontrol according to the seventh embodiment of the present invention.

DESCRIPTION OF REFERENCE SYMBOLS

-   1101, 2101, 3101: host device-   1102, 2102, 3102: PC card slot-   1103, 2103, 3103: PC card terminal-   1104, 2104, 3104: Card Bus connector-   1106, 2106, 3106: baseband processor-   1107, 2107, 3107: memory-   1108, 2108, 3108: transmission circuit-   2112, 3112: transmission-output upper-limit estimation section-   2113, 3113: power supply circuit-   2114, 3114: voltage measurement circuit-   1201: D/A converter-   1202, 1203: transistor-   1204: capacitor-   1205: diode-   1401: terminating circuit-   1402: switch-   1501: resistor-   1502: coil-   1503; capacitor-   S1301 to S1314: steps carried out by a baseband processor in a first    embodiment-   S1601 to 1613: steps carried out by a baseband processor in a second    embodiment-   S2101 to S2109: steps for communication processing in a fourth    embodiment-   S2201 to 2208: steps for communication processing in a fifth    embodiment-   S2301 to 2308: steps for communication processing in a sixth    embodiment-   S3101 to S3104: steps for communication processing in a seventh    embodiment-   S3201 to 33210: steps for communication processing in an eighth    embodiment

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments according to the present invention will now be describedwith reference to the drawings. The current description assumes exampleswhere a 32-bit PC card communication terminal in accordance with theCDMA2000 1×EV-DO standard is used.

FIG. 1 is a schematic block diagram depicting the structure of a PC cardcommunication terminal according to a first embodiment of the presentinvention. In the same figure, reference numeral 1101 denotes a hostdevice, such as a so-called notebook PC, having a PC card slot 1102.Reference numeral 1103 denotes a PC card terminal which includes a32-bit Card Bus connector 1104. This PC card terminal 1103 is mounted inthe host device 1 for use and is supplied with power from the hostdevice 1101 to operate, controlled using, for example, the AT command.

In this PC card terminal 1103, reference numeral 1105 denotes a bridgethat connects a Card Bus and a USB (universal serial bus), referencenumeral 1106 denotes a baseband processor that performs communicationcontrol, reference numeral 1107 denotes a memory used by the basebandprocessor 1106, reference numeral 1108 denotes a transmission circuit,reference numeral 1109 denotes a reception circuit, reference numeral1110 denotes a branching filter, and reference numeral 1111 denotes anantenna. These components are realized by a general structure, and adescription thereof will be omitted.

Reference numeral 1112 denotes a load circuit whose load value changesunder the control of the baseband processor 1106. A specific example ofthis load circuit will be described later. The line of power suppliedfrom the host device 1101 is connected to a power supply circuit 1113and a voltage measurement circuit 1114. The power supply circuit 1113produces voltage to be supplied to components in the card terminal. Inthe figure, only the power supply routes to the transmission circuit1108 and to the load circuit 1112 are shown; power supply routes toother circuits are omitted. The voltage measurement circuit 1114measures a supply voltage under the control of the baseband processor1106.

Furthermore, reference numeral 1112 denotes a transmission-outputupper-limit estimation section that estimates a transmission-outputupper limit, which will be described later. If the baseband processor1106 and a DSP (digital signal processor), not shown in the figure, aremade to read a predetermined program and employ, for example, a methodfor carrying out the above-described estimation processing, thetransmission-output upper-limit estimation section can be realized withan existing hardware configuration.

FIG. 2 is a circuit diagram depicting one specific example of the loadcircuit 1112. In the same figure, reference numeral 1201 denotes a D/Aconverter that performs D/A (digital/analog) conversion of a controlsignal from the baseband processor. Reference numerals 1202 and 1203denote npn transistors. Supply voltage from the power supply circuit isapplied to the collector of each of the transistors 1202 and 1203. Anoutput terminal of the D/A converter 1201 is connected to the base ofthe transistor 1202. The emitter of the transistor 1202 is connected tothe base of the transistor 1203. The emitter of the transistor 1203 isconnected to the ground. A series circuit composed of a capacitor 1204and a diode 1205 connected in series is interposed between the base ofthe transistor 1202 and the ground.

Referring back to FIG. 1, power from the power supply circuit 1113 issupplied selectively to the load circuit 1112 or the transmissioncircuit 1108 under the control of the baseband processor 1106. This maybe achieved by means of a switch 1115 provided outside the power supplycircuit 1113, as shown in the figure, or by turning ON/OFF individualsupply voltages from the power supply circuit 1113 controlled by thebaseband processor 1106.

The operation of the card communication terminal according to thisembodiment will now be described. FIG. 3 is a flowchart illustrating themain part for communication control by the baseband processor Referringto FIGS. 1 and 3, when the power supply is turned ON by inserting the PCcard terminal 1103 into the PC slot 1102 of the host device 1101, thebaseband processor 1106 starts up and carries out predetermined initialsetting first (S1301). The baseband processor 1106 then carries outstandby/communication processing in a normal mode (S1302). In the normalmode, communication is achieved by supplying power to the transmissioncircuit 1108 and performing transmission and reception with the basestation.

In this case, when an instruction for measuring a transmission powerupper limit is given from the host device to the PC card terminal 1103using PC card terminal control means, such as the AT command, via a useroperation or driver function (S1303: Yes), the baseband processor 1106enters a transmission-power upper-limit measurement mode.

In this transmission-power upper-limit measurement mode, the basebandprocessor 1106 follows the procedure described below to carry outprocessing. First, if communication is in progress (S1304: Yes), thecommunication processing is terminated (S1305). Then, the switch 1115 isoperated or the power supply circuit 1113 is controlled to cut off thepower to the transmission circuit 1108 (S1306), and furthermore powersupply to the load circuit 1112 is started (S1307). In this case, theload circuit 1112 is controlled so as to start operation with an initialload value that produces a minimum current setting.

In this state, a measurement voltage value is acquired from the voltagemeasurement circuit 1114 (S1308), and the measurement voltage value iscompared with an operable voltage value preset as a lowest voltage valuewith which the PC card terminal can operate (S1309). If the measurementvoltage value is larger (S1309: Yes), the load value of the load circuit1112 is changed to increase the electric current (S1311) and measurementis carried out again. In this manner, the same procedure is repeated byreturning to step S1308 until the measurement voltage value decreases tothe operable voltage value (S1309: No) or the load value reaches a loadvalue corresponding to the predetermined maximum current (S1310: No).

When the measurement voltage decreases to the operable voltage (S1309:No) or the load value reaches a load value corresponding to the maximumcurrent (S1310: No) in this manner, the baseband processor 1106 refersto a load-value/transmission-output conversion table pre-stored in thememory 1107, acquires a transmission output corresponding to the loadvalue of the load circuit 1112 (S1312), and stores this value as atransmission-output upper limit of the PC card terminal 1103 in the hostdevice 1101 (S1313). Thereafter, measurement completion is reported tothe host device using, for example, a result code of the AT command(S1314) to return to the normal mode (S1302).

The CDMA2000 1×EV-DO standard follows a procedure where the base stationmakes a request to the PC card terminal 1103 for a transmission output.In the normal mode, however, the baseband processor 1106 compares thetransmission output requested by the base station with theabove-described transmission-output upper limit, and even when atransmission output higher than the transmission-output upper limit isrequired (including a case where an output value under open-loop orclosed-loop control exceeds the transmission-output upper limit), thetransmission output is restricted to the transmission-output upper limitto prevent the supply voltage from falling below the operable voltagevalue.

For the relationship between load values of the load circuit 1112 andtransmission outputs, electric currents for transmission outputs of thetransmission circuit 1108 and electric currents for loads of the loadcircuit 1112 are measured for a certain number of units or all unitswhen the PC card terminal 1103 is manufactured to track them asrepresentative values or individual adjustment values, so that theload-value/transmission-output conversion table is produced based onthis data. Furthermore, the operable voltage used in step S1309 of FIG.3 can simply be preset in accordance with, for example, theabove-described standards. In addition, for the load value correspondingto the maximum current used in step S1310 of FIG. 3, it is sufficient toset a load value corresponding to the maximum current value determined,for example, from hardware restrictions of the PC card terminal 1103itself or output restrictions imposed by laws and regulations.Furthermore, for the initial load value used in step S1307, it issufficient to set a load value corresponding to the minimum currentdetermined by taking into consideration a safety margin that is wideenough to prevent the supply voltage from falling below the operablevoltage even if the power supply performance of the host device 1101 islower than the standard. These data are stored in a nonvolatile portionof the memory 1107.

A second embodiment of the present invention will now be described. FIG.4 is a block diagram depicting a PC card communication terminalaccording to the second embodiment. As shown in the same figure, in thesecond embodiment, there are provided a terminating circuit 1401 thatabsorbs transmission outputs of the transmission circuit 1108 to nullifythem and a switch 1402 that selectively connects the output terminal ofthe transmission circuit 1108 to either the branching filter 1110 or theterminating circuit 1401 according to an instruction of the basebandprocessor 1106. On the other hand, the load circuit 1112 and the switch1115 (refer to FIG. 1) provided in the first embodiment are notnecessary. Other components are the same as those in the firstembodiment, and thus a description thereof will be omitted.

FIG. 5 is a circuit diagram depicting one specific example of theterminating circuit. As shown in the same figure, the terminatingcircuit 1401 can be realized by interposing a series circuit composedof, for example, a resistor 1501, a coil 1502, and a capacitor 1503between the input terminal and the ground.

The operation of the baseband processor 1106 according to the secondembodiment will be described. FIG. 6 is a flowchart illustrating themain part for communication control by the baseband processor accordingto the second embodiment.

Referring to FIGS. 4 and 6, when the power supply is turned ON byinserting the PC card terminal 1103 into the PC slot 1102 of the hostdevice 1101, the baseband processor 1106 starts up and carries outpredetermined initial setting first (S1601). The baseband processor 1106then carries out standby/communication processing in a normal mode(S1602). In normal mode communication, the switch 1402 is switched overto the branching filter 1110 to connect the output terminal of thetransmission circuit 1108 to the branching filter 1110 so thatcommunication is achieved by performing transmission and reception withthe base station.

In this case, if an instruction for measuring a transmission power upperlimit is issued from the host device (S1603: Yes), the basebandprocessor 1106 enters the transmission-power upper-limit measurementmode, and if communication is in progress (S1604: Yes), thecommunication processing is terminated (S1605). Thereafter, the switch1402 is operated to connect the output terminal of the transmissioncircuit 1108 to the terminating circuit 1401.

In this state, the transmission circuit 1108 is controlled to performtransmission operation with a minimum current setting (S1607), and ameasurement voltage value is acquired from the voltage measurementcircuit 1114 (S1608). If the measurement voltage value is higher thanthe operable voltage value (S1609: Yes) and the transmission output islower than the maximum transmission output value (S1610: No), the flowreturns to step 1608 to repeat the same procedure.

Then, when the measurement voltage value decreases to the operablevoltage value (S1609: No) or the transmission output reaches the maximumtransmission output value (S1610: No), the baseband processor 1106stores the transmission output value at this time as atransmission-output upper limit. (S1612). Subsequently, measurementcompletion is reported to the host device (S1613) to return to thenormal mode (S1602).

A third embodiment of the present invention will now be described. It isassumed that the host device has a preinstalled OS (operating system)which provides a function for detecting a PC card terminal mounted inthe PC card slot.

When the PC card terminal is inserted in the PC card slot for the firsttime, the host device reads out information such as the device type fromthe PC card terminal to install the corresponding driver software.Thereafter, each time the same card terminal is inserted in the cardslot, the host device reads out the corresponding driver software from,for example, the hard disk to control the card terminal via the driversoftware. The driver software for the card terminal operates as follows.

When driver software is installed (the first time the PC card terminalis controlled), the driver software at least once instructs the PC cardterminal to measure a transmission-output upper limit. The PC cardterminal determines a transmission-output upper limit by following thesame procedure as in the first or second embodiment and reports thetransmission-output upper limit to the driver software using, forexample, a result code of the AT command.

The driver software saves the reported transmission-output upper limitas information specific to that PC card terminal. Subsequently, when thePC card terminal is inserted in the same host device, the driversoftware transmits the saved transmission-output upper limit to the PCcard terminal. The PC card terminal stores the receivedtransmission-output upper limit to restrict the transmission output viacommunication control.

With the above-described structure, a transmission-output upper limit ismeasured only when the PC card terminal is used for the first time,thereby suppressing power consumption by, for example, the notebookpersonal computer functioning as the host device.

Embodiments according to the present invention will now be describedwith reference to the drawings. The current description assumes exampleswhere a 32-bit PC card communication terminal in accordance with theCDMA2000 1×EV-DO standard is used.

FIG. 7 is a schematic block diagram depicting the structure of a PC cardcommunication terminal according to a fourth embodiment of the presentinvention. In the same figure, reference numeral 2101 denotes a hostdevice, such as a so-called notebook PC, having a PC card slot 2102.Reference numeral 2103 denotes a PC card terminal which includes a32-bit Card Bus connector 2104. This PC card terminal 2103 is mounted inthe host device 1 for use and is supplied with power from the hostdevice 2101 to operate, controlled using, for example, the AT command.

In this PC card terminal 2103, reference numeral 2105 denotes a bridgethat connects a Card Bus and a USB (universal serial bus), referencenumeral 2106 denotes a baseband processor that performs communicationcontrol, reference numeral 2107 denotes a memory used by the basebandprocessor 2106, reference numeral 2108 denotes a transmission circuit,reference numeral 2109 denotes a reception circuit, reference numeral2110 denotes a branching filter, and reference numeral 2111 denotes anantenna. These components are realized by a general structure, and adescription thereof will be omitted.

Reference numeral 2112 denotes a transmission-output upper-limitestimation section that performs estimation processing of atransmission-output upper limit, which will be described later. If thebaseband processor 2106 and a DSP (digital signal processor), not shownin the figure, are made to read a predetermined program and employ, forexample, a method for carrying out the above-described estimationprocessing, the transmission-output upper-limit estimation section canbe realized with an existing hardware configuration.

The line of power supplied from the host device 2101 is connected to apower supply circuit 2113 and a voltage measurement circuit 2114. Thepower supply circuit 2113 produces voltage to be supplied to componentsin the card terminal. Power supply routes to components are not shown inthe figure. The voltage measurement circuit 2114 measures a supplyvoltage under the control of the baseband processor 2106.

The operation of the card communication terminal according to thisembodiment will now be described. FIG. 8 is a flowchart illustrating themain part for communication control according to the fourth embodiment.Referring to FIGS. 7 and 8, when the power supply of the PC cardterminal 2103 is turned ON by inserting the PC card terminal 2103 in thePC slot 2102 of the host device 2101, the baseband processor 2106 startsup and is subsequently controlled by the host device 2101 using, forexample, the AT command.

In this manner, a search is made for a base station and standbyoperation is started as with a normal terminal (S2101). When theterminal starts transmission (S2102), such as when a base station isfound and registration in the base station is performed to start tostandby operation or when a call is originated during standby operation,the transmission power is acquired (S2103), and at the same time, thevoltage supplied from the host device 2101 is measured by the voltagemeasurement circuit 2114 (S2104).

The baseband processor 2106 stores this measurement value in the memory2107 and acquires transmission power again (S2105). The transmissionpower acquired at this time is compared with the previously acquiredtransmission power to determine if there is a change (S2106). If thereis no change, monitoring the transmission power for any change iscontinued (S2106: No). If there is a change in the transmission power(S2106: Yes), the supply voltage is measured again by the voltagemeasurement circuit 2114 (S2107). The processing from steps S2105 toS2107 is repeated N-1 times, where N (≧2) represents a value preset asthe number of times the supply voltage needs to be measured to estimatea transmission-output upper limit.

When N measurement values of supply voltage at different transmissionpower levels are acquired as a result of the above-described processing,the transmission-output upper-limit estimation section 2112 calculates atransmission-output upper limit using these N measurement values(S2108). The transmission-output upper limit is an upper limit oftransmission output for restricting the drop in supply voltage to withina range in which the supply voltage does not fall below the permissiblelowest supply voltage of the PC card terminal 2103. Thistransmission-output upper limit is determined depending on therelationship between the supply voltage supplied from the host device2101 and the characteristics of the current consumption of the PC cardterminal (particularly the transmission circuit 2108).

With this transmission-output upper limit, setting for limiting themaximum transmission power of the PC card terminal 2103 is performed(S2109), and then a series of operations ends. In the CDMA2000 1×EV-DOstandard, the base station restricts a transmission output to the PCcard terminal 2103. However, after a transmission-output upper limit hasbeen acquired through the above-described series of operations, thebaseband processor 2106 compares the transmission output restricted bythe base station with the above-described transmission-output upperlimit, and even when a transmission output higher than thetransmission-output upper limit is required (including a case where anoutput value under open-loop or closed-loop control exceeds thetransmission-output upper limit), the transmission output is restrictedto the transmission-output upper limit to prevent the supply voltagefrom falling below the operable voltage value.

When the PC card terminal 2103 ends operation at power OFF, thetransmission-output upper limit is cleared. The next time the powersupply is turned ON, the baseband processor 2106 sets atransmission-output upper limit by following the same procedure.Alternatively, the host device 2101 may store the settransmission-output upper limit so that the stored transmission-outputupper limit can be restored in the PC card terminal 2103 when the PCcard terminal 2103 is to be used again. Furthermore, the same operationmay be carried out, as appropriate, during the subsequent transmissionso that the accuracy of the transmission-output upper limit can beincreased. In the above-described processing, although a transmissionpower value known to the baseband processor 2106 is used when a supplyvoltage measurement value is to be acquired, a measurement section formeasuring the transmission power of the transmission circuit 2108 may beprovided so that a measurement value of this measurement section can beused.

Processing in the transmission-output upper-limit estimation section2112 will be described below in detail. A table representing therelationship between transmission power and current consumption of thePC card terminal 2103 is stored in a nonvolatile portion of the memory2107. It is assumed that to produce this table, the relationship betweentransmission power and current consumption is measured for a certainnumber of PC card terminals 2103 or all PC card terminals 2103 at thetime of shipment and tracked as representative values or individualadjustment values.

FIG. 9 is a diagram depicting one example of a table representing thecorrespondence between transmission power and current consumption. Thisrelationship may be stored in the form of a table representingtransmission power and current consumption, as shown in the figure, ormay be stored in the form of a function expression such as I=F (W),where I represents current consumption and W represents transmissionpower.

FIG. 10 is a graph depicting the relationship between supply voltage andcurrent consumption. The current description assumes that N measurementresults supplied from the baseband processor are N=5. Symbols m1 to m5represent measurement values, VM represents an operable voltage value,and iM represents a current consumption value corresponding to theoperable voltage value VM. The operable voltage value VM represents aminimum value of supply voltage required to allow the PC card terminalto operate normally. This value VM is assumed to be prestored in thememory 2107 (refer to FIG. 7).

As shown in FIG. 10, the current consumption and the supply voltageexhibit a certain degree of linearity. Therefore, with two or moremeasurement values, the current consumption value iM as indicated whenthe supply voltage is equal to the operable voltage value VM can bedetermined. Thus, the current consumption value iM is estimated firstfrom the five measurement values m1 to m5. Next, transmission powercorresponding to the current consumption value iM is acquired using theabove-described table or function expression to set it as an estimatedtransmission-output upper limit.

Referring back to FIG. 7, a transmission power upper limit for allowingthe PC card terminal 2103 to operate normally in the host device 2101 isestimated through the above-described operation. By setting this valueas the maximum transmission power of the PC card terminal 2103, the PCcard terminal 2103 can be prevented from being reset or fromexperiencing unstable operation due to a decrease in the suppliedvoltage without concern on the user's part. Furthermore, since atechnique for setting a transmission-output upper limit when requestedtransmission processing is performed is employed, the need fortransmission operation only for setting a transmission-output upperlimit can be eliminated. This allows processing to be carried outwithout increasing power consumption by, for example, the notebook PCfunctioning as the host device.

A fifth embodiment of the present invention will now be described. Thefifth embodiment can be realized with an apparatus outline structuresimilar to that in the fourth embodiment shown in FIG. 7, and thus adescription of the apparatus outline structure will be omitted. Thefifth embodiment differs from the fourth embodiment in processing of thebaseband processor. This processing is described below.

FIG. 11 is a flowchart illustrating the main part for communicationcontrol according to the fifth embodiment of the present invention. Asshown in FIGS. 7 and 11, when the power supply of the PC card terminal2103 is turned ON by inserting the PC card terminal 2103 in the PC slot2102 of the host device 2101, the baseband processor 2106 starts up andis subsequently controlled by the host device 2101 using, for example,the AT command.

Next, if transmission is required, transmission processing is started(S2202). It is assumed, however, that transmission is not performed inthe transmission processing startup of step S2202. Thereafter, thememory 2107 is referred to to determine if there is a transmissionhistory after power ON (S2203). If there is a transmission history(S2203: Yes), it is determined that an appropriate transmission-outputupper limit has already been acquired, and thus the flow proceeds to thenormal transmission operation (S2208).

If there is no transmission history, indicating that this is the firsttransmission (S2203: No), the initial transmission power is decreased bya predetermined value stored in the memory 2107 (S2204). Thispredetermined value may be a constant value, such as “20 dBm.”Alternatively, the predetermined value may be variable depending on theinitial transmission power, such as “10 dBm” for initial transmissionpower<0 dBm, “20 dBm” for 0 dBm≦initial transmission power<10 dBm, or“30 dBm” for 10 dBm≦initial transmission power. Furthermore, thepredetermined value may be determined as “−20 dBm−initial transmissionpower.” By doing so, a safety margin wide enough to prevent the supplyvoltage of the PC card terminal 2103 from falling below the operablevoltage is ensured even when the power supply performance of the hostdevice 2101 is lower than the standard. Transmission is started with theinitial transmission output determined in this manner (S2205).

Next, measurement of transmission power and supply voltage is repeatedseveral times while the transmission power is increased in predeterminedsteps of the transmission output, and a transmission-output upper limitis acquired in an area where the transmission power is low. Then, thetransmission-output upper limit is set in the PC card terminal 2103(S2206). The transmission-output upper limit is calculated in the samemanner as in the fourth embodiment. The above-described increment oftransmission power is preset as a smallest possible value, taking intoconsideration the estimation accuracy of the transmission-outputupper-limit estimation section. Thereafter, a transmission history iswritten in the memory 2107 (S2207). Subsequently, normal transmission iscarried out while the maximum transmission power is controlled by meansof the transmission-output upper limit (S2208).

In the CDMA2000 1×EV-DO standard, the initial transmission power isdetermined based on the reception power of the terminal. If thereception power is sufficiently intense, the base station is assumed tobe located nearby so that low transmission power is set to avoidinterference with other terminals. On the other hand, in a weakelectrical field, high transmission power is set to access the basestation because the base station is located far away. For this reason,it is possible that transmission starts with high transmission powerimmediately after the PC card terminal is inserted in the host device.

According to the fifth embodiment, even in such a case, atransmission-output upper limit is set while the transmission power islow, and then normal transmission is initiated. Therefore, the PC cardterminal 2103 can be prevented from being, for example, reset due tohigh transmission output.

A sixth embodiment of the present invention will now be described. Asdescribed above, according to CDMA2000 1×Ev-DO, the predeterminedprocedure described below is followed when the base station is to beaccessed. First, transmission power is determine based on the receptionpower. Next, transmission called an access probe is carried out for apredetermined period of time with that transmission power. At this time,communication between the base station and the terminal is started ifthere is a response from the base station. If there is no response, thetransmission power is increased by a predetermined value to transmitanother access probe. This process is repeated until a response isreceived from the base station. In this case, increasing thetransmission power is not continued, but this process is repeated whilethe transmission power is increased the number of times determined bythe base station, and then transmission is started again with thetransmission power determined from the reception power transmission.Thereafter, this is repeated until a response is received from the basestation. If no response is received while this operation is repeated acertain number of times, transmission is aborted. In the sixthembodiment, a transmission-output upper limit is set in this accessprobe, and will be described below.

FIG. 12 is a flowchart illustrating the outline of communicationprocessing according to the sixth embodiment of the present invention.As shown in FIGS. 7 and 12, when the power is turned ON as a result ofthe PC card terminal 2103 being inserted in the host device 2101,reception operation is carried out to search for a base station in thevicinity (S2301). When a base station is found, transmission operationis started for registration in the base station. At this time, thetransmission power is set to a lowest value (e.g., −25 dBm) (S2302) andone access probe is transmitted (S2303). While the access probe is beingtransmitted, transmission power and supply voltage are measured (S2304,S2305). Thereafter, the transmission power is increased by thetransmission output increment value (e.g., 1 dB) (S2306), and asubsequent access probe is transmitted (S2303). The processing fromsteps S2303 to S2308 is repeated N times to acquire N measurementresults. A transmission-output upper limit is set in the same manner asin the fourth embodiment (S2307), and access to the base station iscontinued with normal transmission power (S2308).

FIG. 13 is a graph depicting an exemplary operation according to thesixth embodiment of the present invention. In the figure, the horizontalaxis represents time, and the vertical axis represents transmissionpower. Unshaded areas represent the original transmission power withwhich transmission should be performed in an access probe, whereasshaded areas represent transmission power with which actual transmissionis performed. As shown in the figure, when transmission is started, anaccess probe is transmitted not with the original transmission power butwith the minimum transmission power. Thereafter, the transmission poweris increased in a stepwise manner, access probe is continued, Nmeasurement results are obtained, and a transmission-output upper limitis set. Then, access probe is carried out with the original transmissionoutput. If the transmission output exceeds the transmission-output upperlimit, the transmission output is restricted to the transmission-outputupper limit for transmission.

As described above, since a transmission-output upper limit can be setduring access probe available to the known method, a transmission-outputupper limit can be set for a short period of time without concern on theuser's part.

Embodiments according to the present invention will now be describedwith reference to the drawings. The current description assumes exampleswhere a 32-bit PC card communication terminal in accordance with theCDMA2000 1×EV-DO standard is used.

FIG. 14 is a schematic block diagram depicting the structure of a PCcard communication terminal according to a seventh embodiment of thepresent invention. In the same figure, reference numeral 3101 denotes ahost device, such as a so-called notebook PC, having a PC card slot3102. Reference numeral 3103 denotes a PC card terminal which includes a32-bit Card Bus connector 3104. This PC card terminal 3103 is mounted inthe host device 1 for use and is supplied with power from the hostdevice 3101 to operate, controlled using, for example, the AT command.

In this PC card terminal 3103, reference numeral 3105 denotes a bridgethat connects a Card Bus and a USB (universal serial bus), referencenumeral 3106 denotes a baseband processor that performs communicationcontrol, reference numeral 3107 denotes a memory used by the basebandprocessor 3106, reference numeral 3108 denotes a transmission circuit,reference numeral 3109 denotes a reception circuit, reference numeral3110 denotes a branching filter, and reference numeral 3111 denotes anantenna. These components are realized by a general structure, and adescription thereof will be omitted.

Reference numeral 3112 denotes a transmission-power upper-limitcalculation section for calculating a transmission power upper limit. Ifthe baseband processor 3106 and a DSP (digital signal processor), notshown in the figure, are made to read a predetermined program andemploy, for example, a method for carrying out predetermined calculationprocessing, the transmission-power upper-limit calculation section canbe realized with an existing hardware configuration.

The line of power supplied from the host device 3101 is connected to apower supply circuit 3113 and a voltage measurement circuit 3114. Thepower supply circuit 3113 produces voltage to be supplied to componentsin the card terminal. Power supply routes to components are not shown inthe figure. The voltage measurement circuit 3114 measures the supplyfrom the host device 3101 under the control of the baseband processor3106.

The operation of a card communication terminal according to thisembodiment will now be described. FIG. 15 is a flowchart illustratingthe main part for communication control according to the seventhembodiment. Referring to FIGS. 14 and 15, when the power supply of thePC card terminal 3103 is turned ON by inserting the PC card terminal3103 in the PC slot 3102 of the host device 3101, the baseband processor3106 starts up and performs communication processing by following theprocedure below.

First, the baseband processor 3106 performs transmission startprocessing before starting transmission (S3101). During the transmissionprocessing, transmission power is determined, for example, from thereception power and the transmission power to start transmission(S3102). When transmission is performed, the transmission-powerupper-limit calculation section 3112 measures a supply voltage VS usingthe voltage measurement circuit 3114 and compares the result with athreshold VT (S3103). The threshold VT is a value where a margin Vm istaken into consideration for a permissible lowest supply voltage valueVM (=VM+Vm). The margin Vm is a value for setting a voltage range basedon which it is determined that the supply voltage VS is sufficientlyclose to but not below the permissible lowest supply voltage value VM.

The permissible lowest supply voltage value VM is a value preset as apermissible lowest value of the supply voltage at which the internalcircuit of the PC card terminal 3103 can operate normally. This valuemay be set in accordance with the standard or may be set as arepresentative value or an individual adjustment value by performingoperation check of a certain number of PC card terminals 3103 or all PCcard terminals 3103 at the time of shipment. In addition, if asufficiently wide margin can be expected for the permissible lowestsupply voltage value VM, such as when there is a margin for the limitvalue although a standard value has been employed as the permissiblelowest supply voltage value VM, then the permissible lowest supplyvoltage value VM can be set as the threshold VT without providing themargin Vm.

If it is determined in step S3103 that the supply voltage VS is largerthan the threshold VT (S3103: Yes), the terminal can successfullyoperate and therefore continues transmission. Thereafter, the processingin step S3102 and the subsequent processing are repeated until thetransmission ends. Furthermore, if it is determined in step S3103 thatthe supply voltage VS is equal to or lower than the threshold VT (S3103:No), it indicates that the transmission power at this time is close to alimit at which the internal circuit of the PC card terminal 3103 cannormally operate and furthermore, transmission has already beenperformed normally. Thus, the transmission power at this time is storedin the memory 3107 as a transmission power upper limit, setting forcontrolling the maximum transmission power of the PC card terminal 3103using this transmission power upper limit (S3104) is performed, and aseries of operations end.

In the CDMA2000 1×EV-DO standard, the base station restrictstransmission power to the PC card terminal 3103. However, after atransmission power upper limit has been acquired through theabove-described series of operations, the baseband processor 3106compares the transmission power restricted by the base station with theabove-described transmission power upper limit, and even whentransmission power higher than the transmission power upper limit isrequired (including a case where an output value under open-loop orclosed-loop control exceeds the transmission power upper limit), thetransmission power is restricted to the transmission power upper limitto prevent the supply voltage from falling below the operable voltagevalue.

When the PC card terminal 3103 ends operation at power OFF, thetransmission power upper limit is cleared. The next time the powersupply is turned ON, the transmission-power upper-limit calculationsection 3112 sets a transmission power upper limit by following the sameprocedure. Alternatively, a transmission power upper limit that has beenset may be stored by the host device 3101 so that the storedtransmission power upper limit may be restored in the PC card terminal3103 when the PC card terminal 3103 is to be used again.

By obtaining a transmission power upper limit at which the PC cardterminal 3103 can normally operate with the power supply performance ofthe host device 3101 and then setting the value as the maximumtransmission power of the PC card terminal 3103 through theabove-described operation, the PC card terminal 3103 can be preventedfrom being reset or from experiencing unstable operation due to adecrease in the supplied voltage without imposing particular operationupon the user. Furthermore, since a technique for setting a transmissionpower upper limit during transmission processing is employed, the needfor transmission operation only for setting a transmission power upperlimit is eliminated. This affords an advantage in that, for example, thenotebook PC functioning as the host device is saved from having toparticularly increase power consumption.

An eighth embodiment of the present invention will now be described. Theeighth embodiment can be realized with an apparatus outline structuresimilar to that in the seventh embodiment shown in FIG. 14, and thus adescription of the apparatus outline structure will be omitted. Theeighth embodiment differs from the seventh embodiment in arithmeticoperation of a transmission power upper limit, which is described below.

FIG. 16 is a flowchart illustrating the main part for communicationcontrol according to the eighth embodiment. Referring to FIGS. 14 and16, when the card terminal is to perform transmission, the basebandprocessor 3106 first enters transmission processing (S3201). After thetransmission processing has been entered, the baseband processor 3106calculates and determines transmission power for transmission based on,for example, the reception state and base station's instruction (S3202).Next, the transmission history in the memory 3107 is referred to(S3203).

Here, the transmission history is information to be written to thememory 3107 in step S3208, which will be described later. Morespecifically, a highest transmission power value WM, which is thelargest of all transmission power values after the PC card terminal 3103has been turned ON so far, is written. This transmission history may beadditionally provided with, for example, the supply voltage VS at thetime of transmission with the highest transmission power value WM. Inshort, it is sufficient if transmission history includes the highesttransmission power so far and information indicating that the supplyvoltage VS at that time is below the threshold VT.

Thereafter, the transmission power determined in step S3202 is comparedwith a trial transmission power value WT (maximum transmission powervalue WM+predetermined value ΔW) (S3204). Here, the predetermined valueΔW is a trial increment of the transmission power for ensuring that theamount of drop in the supply voltage VS is within the margin Vm, and cansimply be set to a sufficiently small value (e.g., 1 dB) to leave a widemargin.

As a result, if the current transmission power is larger than the trialtransmission power value WT (S3204: Yes), the trial transmission powervalue WT is set to the transmission power (S3205) to performtransmission (S3206). Furthermore, if the current transmission power issmaller than the trial transmission power value WT (S3204: No),transmission is performed with the current transmission power (S3206).

Thereafter, the transmission power with which transmission has beenperformed this time is compared with the highest transmission powervalue WM (S3207). If the current transmission power exceeds the highesttransmission power value WM (S3207: Yes), the transmission history isupdated with the current transmission power as the highest transmissionpower value WM (S3208). If the current transmission power is below thehighest transmission power value WM (S3207: No), the flow proceeds tothe next step without updating the transmission history. For the initialvalue of the transmission history, a sufficiently small transmissionpower value can simply be set.

Thereafter, the supply voltage VS at that transmission power is measuredby the voltage measurement circuit 3114 to compare it with the thresholdVT (S3209). If the supply voltage VS is below the threshold VT as aresult, the current transmission power is set to a transmission powerupper limit, confidently assuming that the current transmission power isan output sufficiently close to a limit at which normal transmissionoperation is possible with the power supply performance of the hostdevice 3101 (S3210). If the supply voltage VS exceeds the threshold VT(83209: No), the flow returns to step S3202, assuming that the outputstill has a margin, and processing is continued without setting atransmission power upper limit.

For the CDMA2000 1×EV-DO standard, the initial transmission power isdetermined based on the reception power of the terminal. If thereception power is sufficiently intense, the base station is assumed tobe located nearby so that low transmission power is set to avoidinterference with other terminals. On the other hand, in a weakelectrical field, high transmission power is set to access the basestation because the base station is located far away. For this reason,it is possible that transmission starts with high transmission powerimmediately after the PC card terminal is inserted in the host device.

According to the eighth embodiment, even in such a case, transmission iscarried out while the trial transmission power value WT is increased ina stepwise manner starting at a low transmission power level, andtherefore, the PC card terminal 3103 can be prevented from being, forexample, reset not only after but also before a transmission power upperlimit is set.

Although embodiments of the present invention have been described withreference to the drawings, specific structures are not limited to theseembodiments. Instead, design without departing from the spirit and scopeof the present invention also constitutes the present invention.

1. A method of controlling a wireless communication terminal that issupplied with power supply from a host device for operation, thewireless communication terminal being mounted in the host device, themethod comprising the steps of: measuring a voltage of the power supply;setting a transmission-output upper limit based on the voltage; andrestricting a maximum transmission output based on thetransmission-output upper limit.
 2. The method of controlling a wirelesscommunication terminal according to claim 1, the method comprising thestep of measuring a drop in the voltage corresponding to currentconsumption while transmission is not being performed, wherein, in thestep of setting the transmission-output upper limit, a transmissionoutput that occurs when the voltage decreases to a preset permissiblelowest voltage is obtained to set the transmission output as thetransmission-output upper limit.
 3. The method of controlling a wirelesscommunication terminal according to claim 2, wherein, in the step ofmeasuring the drop in the voltage, the drop in the voltage is measuredvia a load value of a load circuit, the load value being variable, whilethe voltage is applied to the load circuit, and in the step of settingthe transmission-output upper limit, the transmission-output upper limitis set by converting the load value into a transmission output.
 4. Themethod of controlling a wireless communication terminal according toclaim 2, wherein, in the step of measuring the drop in the voltage, thedrop in the voltage is set by measuring the drop in the voltage with aterminating circuit for terminating a transmission output beingconnected to a transmission circuit.
 5. The method of controlling awireless communication terminal according to claim 1, wherein thewireless communication terminal includes: a transmission-outputupper-limit mode in which the transmission-output upper limit is set andthe set transmission-output upper limit is transmitted to the hostdevice and saved; and a normal communication mode in which the maximumtransmission output is restricted based on the transmission-output upperlimit received from the host device, and one of the transmission-outputupper-limit mode and the normal communication mode is selected.
 6. Themethod of controlling a wireless communication terminal according toclaim 1, wherein, in the step of measuring the voltage, the voltage ismeasured during transmission operation to acquire voltage measurementvalues corresponding to different transmission output values, whereinthe method comprises the steps of: converting the transmission outputvalues into current consumption values; and estimating a currentconsumption value corresponding to a preset permissible lowest voltagebased on the voltage values and the current consumption values, and inthe step of setting the transmission-output upper limit, the estimatedcurrent consumption value is converted back into a transmission outputvalue to set the transmission output value as the transmission-outputupper limit.
 7. The method of controlling a wireless communicationterminal according to claim 6, wherein, in the step of measuring thevoltage, transmission operation is performed with a transmission outputlower than a transmission output requested at the time of a firsttransmission operation, and subsequently, the voltage measurement valuesare acquired while the transmission output is increased in a stepwisemanner.
 8. The method of controlling a wireless communication terminalaccording to claim 1, wherein, in the step of measuring the voltage, avoltage value of the power supply is measured during transmissionoperation, and in the step of setting the transmission-output upperlimit, a transmission output value during transmission operationexhibited when the measured voltage value falls below a threshold valuelarger than a preset permissible lowest voltage value is set as thetransmission-output upper limit.
 9. The method of controlling a wirelesscommunication terminal according to claim 8, wherein a maximumtransmission output value with which transmission has been performed isstored as a maximum transmission-output history value before the step ofmeasuring a voltage value of the power supply; and if a transmissionoutput with which transmission is to be performed exceeds the maximumtransmission-output history value, the transmission output is restrictedto a value produced by adding a predetermined increment value to themaximum transmission-output history value, and after the transmission,the maximum transmission-output history value is updated.
 10. A programfor a wireless communication terminal, the program achieving the methodof controlling a wireless communication terminal according to claim 1.11. A wireless communication terminal mounted in a host device andsupplied with power supply from the host device for operation,comprising: a supply-voltage measurement section for measuring a voltagevalue of the power supply; a transmission-output upper-limit settingsection for setting a transmission-output upper limit based on thevoltage value; and a transmission-output control section for restrictinga maximum transmission output based on the transmission-output upperlimit.
 12. The wireless communication terminal according to claim 11,comprising: a load circuit having a variable load value; apower-supply-connection switching section for switching a connection ofthe power supply between a transmission circuit and the load circuit; aload-value setting section for determining a load value exhibited whenthe voltage measured by the supply-voltage measurement section while theload value of the load circuit is being changed decreases to a presetpermissible lowest voltage value; and a transmission-output upper-limitconversion section for converting the load value determined by the loadsetting section into the transmission-output upper limit based on aconversion table of a preset load value and the transmission-outputupper limit.
 13. The wireless communication terminal according to claim11, comprising: a terminating circuit for terminating a transmissionoutput; and an output-stage switching section for switching a connectionof an output stage between an antenna and the terminating circuit,wherein the transmission-output upper-limit setting section determines,as the transmission-output upper limit, a transmission output valueexhibited when the voltage measured by the supply-voltage measurementsection while the transmission output is being changed decreases to apreset permissible lowest voltage value.
 14. The wireless communicationterminal according to claim 11, wherein the supply-voltage measurementsection measures voltage values corresponding to different transmissionoutput values during transmission operation, the wireless communicationterminal comprising: a transmission-output/current relationship storagesection storing a correspondence between a transmission output andcurrent consumption; and a current-consumption-value estimation sectionfor estimating a current consumption value corresponding to a presetpermissible lowest voltage value based on the measured voltage valuesand current consumption values obtained by converting the transmissionoutput values using the correspondence in thetransmission-output/current relationship storage section, and thetransmission-output upper-limit setting section converts the currentconsumption value estimated by the current-consumption-value estimationsection back into a transmission output value to set the transmissionoutput value as the transmission-output upper limit.
 15. The wirelesscommunication terminal according to claim 11, wherein the supply-voltagemeasurement section measures voltage values corresponding to differenttransmission output values during transmission operation, and thetransmission-output upper-limit setting section sets, as thetransmission-output upper limit, a transmission output value duringtransmission operation exhibited when the measured voltage value fallsbelow a threshold value larger than a preset permissible lowest voltagevalue.